Human stroke results in multi-organ systemic disease, rather than in solely a brain lesion. While patients may survive the initial brain insult, many succumb to CNS injury-induced immunodepression and fatal infection. Using a murine middle cerebral artery occlusion (MCAO) model of stroke, we found that cerebral ischemic injury leads to bi-phasic consequences for the immune system: early systemic activation of the peripheral immune system, including inflammatory myelin-reactive T cells, followed by a delayed phase of immunopathology associated with massive and progressive splenic apoptosis and loss or re-distribution of remaining immune cells. While this second phase may not directly influence infarct size, exhaustion of immunocompetent cells results in an inability to respond to antigenic challenges. Our overall hypothesis is that peripheral T lymphocytes are major contributors to brain damage after ischemia and to the systemic immunopathology that evolves in tandem. If so, therapy that can block early immune system activation and modulate immunocytes specific for brain antigens would be highly beneficial to stroke survivors. To address this hypothesis, we will utilize our newly developed "designer" recombinant T cell receptor ligand (RTL) platform technology to selectively modulate the inflammatory function of individual myelin-reactive T cell specificities. To test this hypothesis, we propose to 1) determine if RTL551 modulation of the inflammatory activity of brain antigen sensitized T cells results in reduced lymphocyte infiltration into brain and improved outcomes after MCAO in animals of both sexes. Milestone: RTL551 is protective in both sexes and inhibits translocation of GFP+ T cells into brain after MCAO;2) determine if RTL551 improves peripheral immune dysfunction after MCAO in male and female mice. Milestone: RTL551 will improve splenocyte numbers and suppress cytokine-induced splenic apoptosis and immunosuppression after MCAO;and 3) develop a stroke treatment model in humanized DR2 transgenic mice and evaluate treatment effects and requirements for MHC and myelin specificity of RTL1000, an HLA-DR2/MOG-35-55 construct currently being tested in Phase I safety studies in patients with multiple sclerosis. Milestone: RTL1000 will treat MCAO and prevent immunosuppression in DR2 Tg mice. If effective in murine stroke, the RTL approach could be applied rapidly to human stroke patients. Our RTL construct for MS, RTL1000, is comprised of the HLA-DR2 moiety linked to the hMOG- 35-55 peptide, and currently is in FDA approved Phase I safety studies. The RTL1000 could be tested in DR2+ stroke patients relatively soon if the Phase I trial shows this construct to be safe. PUBLIC HEALTH RELEVANCE: Human stroke results in multi-organ systemic disease, rather than in solely a brain lesion. While patients may survive the initial brain insult, many succumb to stroke induced immunodepression caused by an initial over reaction of the immune system. We seek to develop a stroke therapy that would block the initial immune system over activation and thus be highly beneficial to stroke survivors.